A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool equipment, or another process stream (such as air or process water). As a necessary by-product, refrigeration creates waste heat that must be exhausted to ambience, or for greater efficiency, recovered for heating purposes.Chillers may use hermetic scroll, or semi hermetic screw, or centrifugal compressors.

Chilled water is used to cool and dehumidify air in mid- to large-size commercial, industrial, and institutional facilities. Water chillers can be water-cooled, air-cooled, or evaporatively cooled. Water-cooled systems can provide efficiency and environmental impact advantages over air-cooled systems.

Types of Industrial Chillers

Water-Cooled Chillers

Water chillers remove heat by pumping water through a sealed condenser and dispersing it through the cooling tower. Water-cooled chillers are typically more efficient than air-cooled chillers. Using water evaporation to dissipate heat uses significantly less energy than blowing air across a hot surface. This is thanks to water’s high heat capacity. Additionally, water chillers tend to last longer than air-cooled chillers.

Air-Cooled Chillers

Air cooled chillers use air to remove heat by using fans to force air across the exposed tubes of the condenser. While air chillers require more energy than water-cooled chillers, they can be a great option when it comes to stationary cooling. Air chillers are easy to instal and typically can be installed outside a building (no extra space requirements). Compared to water chillers, air chillers are more prone to blockages and recirculation issues.

How Do Chillers Work?

Chillers transfer heat away from a space that requires climate control much like a traditional split system or package unit does, but they use water (or a water solution) to do so instead of air. There are two types of chillers: water-cooled and air-cooled. They work similarly throughout most of the process until the refrigerant reaches the condenser, and both are outlined in the following sections.

Water-Cooled Chillers

The cooling process begins when water enters the evaporator from the primary return where heat is transferred from the water to the refrigerant.

The now-chilled water is then sent to the water tank via the primary supply (shown in blue), where it is distributed to the various climate-controlled spaces by the water pump. Because heat always moves from hot to cold as stated by the second law of thermodynamics, the chilled water absorbs the conditioned space’s ambient heat in the air handler. A fan then forces the cooled air into the space via the ductwork. The warmer water is then returned to the chiller to be cooled once again.

In the meantime, the heat absorbed by the refrigerant (path shown in green) in the evaporator needs to be transferred to allow the refrigerant to absorb more heat. The low-pressure, high-temperature refrigerant moves from the evaporator to the motor-run compressor, which increases the pressure and temperature.

After that, the refrigerant enters the condenser. Water-cooled chillers use water to surround the refrigerant pipes and draw in the heat (path shown in red). The water is then pumped into a cooling tower to release the heat. After condensing, the refrigerant goes through an expansion valve to reduce pressure (and temperature) before returning to the evaporator, where the process begins again.

Air-Cooled Chillers

Like with water-cooled chillers, the process begins with the primary return bringing warm water to the chiller. Heat is transferred in the evaporator to the refrigerant, and the water runs through the primary supply to the cooled space. The refrigerant moves through the compressor to raise the pressure and temperature, and then it reaches the condenser. Here, fans circulate outside air through the condenser, which absorbs heat from the refrigerant (again, the second law of thermodynamics dictates that hot moves to cold) before expelling this heat to the ambient air. The refrigerant then goes through the expansion valve (as before) and returns to the evaporator.

Where Are Chillers Used?

Chillers have several uses and are sometimes preferred over traditional split systems or package units because the water conducts heat better than air. This is also why water-cooled chillers are known for being more consistent and efficient in their performance and for having a longer lifespan than their air-cooled counterparts. Water-cooled chillers are common in medium and larger facilities (so long as they have an adequate water supply), such as airports, hospitals, hotels, shopping malls, commercial buildings, and more.

Air-cooled chillers are more prevalent in small to medium sized facilities where space and water may be limited. The costs to install and maintain these chillers are lower than that of their water-cooled counterparts, but they typically have a shorter lifespan. These chillers are commonly used for restaurants, corporate and sporting events, and temporary structures.

Chillers are also often used for industrial or medical applications. Assembly equipment, construction sites, lasers, MRI machines, and various other high-powered equipment and facilities may require chillers to maintain a workable temperature.

What’s the Difference Between Water-Cooled and Air-Cooled Chillers?

Two main types of industrial chillers exist: water-cooled and air-cooled. Though both chiller types cool industrial process fluids, how the system rejects the extracted heat differs. The needs of the overall refrigeration system therefore determine the best chiller model. Understanding these various strengths makes choosing a proper system design easier.

Chiller Operation Overview

All industrial chillers have the same basic components: evaporator, compressor, expansion device and condenser. They utilize a closed loop refrigeration circuit to cool a fluid (typically water or a water/glycol mixture). The compressor circulates the refrigerant through the closed loop, from condenser to expansion device to the evaporator and, finally, back to the compressor.  As the refrigerant flows through the circuit, the expansion device, usually a valve or a capillary tube, meters it. The evaporator extracts the heat, lowering the fluid temperature and raising the refrigerant temperature. The closed loop system means that the extracted heat must be expelled elsewhere from the system. This role falls to the condenser.  Refrigerant heated by the evaporator fluid and the compressor, enters the condenser. How the condenser cools the refrigerant determines the key difference between water-cooled and air-cooled chillers.

Differences in the Condenser

Air-cooled chillers have condensers that use ambient air to cool hot refrigerant. They are similar in construction to the radiator on a car or the outdoor portion of a home air conditioner.  Refrigerant flows through a series of tubes mechanically assembled with an array of closely spaced fins.  A fan blows ambient air through the fins and over the outside of the tubes, cooling the refrigerant flowing inside. The excess heat is released to the air and can be recovered for use elsewhere in the facility.

Contrastingly, water-cooled chillers use water to cool the refrigerant in the condenser. Water-cooled condensers are typically tube-in-tube, tube-in-shell, or plate-type heat exchangers in which water from a cooling tower or other water source cools the refrigerant.  The refrigerant and cooling water do not come in direct contact with each other, rather they flow in separate passageways within the heat exchanger which are in close contact for efficient heat transfer. The water flows over the refrigerant tubes and absorbs the excess heat, thus lowering the refrigerant to the necessary temperature for use in the system.

Environmental Installation considerations

Though a great deal of variety exists within both air-cooled and water-cooled chillers, some general installation rules do apply. Knowing the ultimate arrangement of a system can help to guide your chiller choice. For each of the following situations, the most practical chiller type is described.

Indoor areas:

Both air-cooled and water-cooled chillers are installable indoors. However, the chiller type will dictate the room’s arrangement. Indoor air-cooled chillers need ventilation to the outside. Sufficient fresh make-up air allows for the maintenance of a suitable temperature within the space. Water-cooled chillers do not require ventilation or fresh make-up air. They are almost exclusively installed indoors. Since they use water for cooling, the water conducts the heat out of the room, eventually exhausted to ambient, often via a cooling tower.

Outdoor Areas:

Almost all outdoor installations will be air-cooled chillers . In these installations, the heat rejected at the condenser simply dissipates into the ambient air. Outdoor installations require properly configured electrical control panels, based on the expected range of environmental conditions.

High Temperature Environments:

Water-cooled chillers work great in high temperature environments since they do not rely on ambient air for cooling.  Thus, they can be placed in hot mechanical rooms or in spaces with minimal ventilation.

Small Spaces:

The condenser on water-cooled chillers is more compact than an equivalently sized air-cooled unit.  This can result in an overall smaller unit, especially in the case of high capacity chillers. However, the entire refrigeration system will still require sufficient space.

Water-scarce areas:

Use an air-cooled unit. The cooling medium, ambient air, does not require any connections. Nor does a chiller with an air-cooled condenser need a cooling tower. These installations have lower overall environmental concerns surrounding water treatment and removal. An air-cooled chiller should be the best choice for water conservation.

Cost considerations

As with any equipment purchase, price will be a consideration. However, the difference in initial cost between an air-cooled and a water-cooled chiller may be misleading. Instead, it is important to factor in all lifetime costs to create the most accurate comparison.

With indoor installation of an air-cooled chiller, costs associated with duct work, fans, and controls for maintaining proper air temperature in the room may exist. Energy consumption costs may be higher for these chiller models due to its basic operating design.

Often times water-cooled units have a lower initial price. However, they generally have more operational costs, and will typically require the installation of a cooling tower. When using a cooling tower in conjunction with a water-cooled chiller, additional costs may accrue from the regular monitoring of water quality, treatment of the water, and the operation of fans and pumps. However, water-cooled chillers allow the refrigeration system to operate at lower head pressure, making them more efficient and less costly to operate than air-cooled chillers.

Factors such as water costs, efficiency ratings, and electricity can dramatically change the lifetime price of a chiller.

Which one do I choose?

If you are uncertain about how to select the right chiller for your system, our cooling engineering experts are always available to help.  Use these sizing factors to gain quick insight into what your system requires.

If after all these considerations, you still cannot make a decision, focus on cooling capacity. Use the process itself to determine the required cooling amount. This is the number one factor in determining the proper chiller size for your system.

Choosing between water-cooled and air-cooled chillers is not an easy process.  However, with the right support and expertise, working through your system’s individual needs will lead to the best equipment purchase for YOU.

Be sure to explore the main chiller options available from Chase Cooling Systems.

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